1. Technical Field
The present invention relates to a PWM control circuit, a flyback converter, and a method for controlling a PWM. More specifically, the present invention relates to a PWM control circuit storing a peak value of one period of a feedback signal from a secondary side output and then, using the stored peak value for a PWM control of a next period, a flyback converter, and a PWM control method.
2. Description of the Related Art
A lighting apparatus using an LED has an advantage of longer lifespan, lower power consumption, or the like, as compared with the existing lighting apparatuses. In order to implement the lighting apparatus using the LED, various structures have been researched and developed.
A circuit for driving the existing LED usually takes a structure of supplying constant voltage or current to the LED constant. For example, in order to isolate a primary side from a secondary aide, a flyback structure, a forward structure, and the like, using a transformer have been used. Further, a buck structure, a buck-boost structure, and so on, which do not isolate the primary side from the secondary side have been used.
In order to implement a constant voltage structure or a constant current structure, there is a need to sense current or voltage of the secondary side and then, reflect the sensed current or voltage to a signal compares with reference voltage through an error amplifier and an output from the error amplifier again compares with a ramp signal, thereby generating the PWM control signal.
The structure may remarkably reduce line regulation characteristics when a period of input voltage is constant but a magnitude thereof is changed.